1. Field of the Invention
The present invention relates to a rolling mill for rolling a plate, and more particularly to a plate rolling mill using work rolls of small diameters and suitable for rolling a hard or ultra-thin strip.
2. Description of the Related Art
In such a rolling mill, using work rolls of smaller diameters provides a larger rolling limit (i.e., enables a plate to be rolled more thinly). For that reason, work rolls of small diameters have been heretofore used for rolling a hard or ultra-thin strip of, e.g., stainless steel. With a decrease in diameter of the work rolls, however, the torsional strength of the rolls themselves lowers inevitably, and a torque required for rolling cannot be applied to the work rolls in some cases. It is hence general that when using work rolls of small diameters, other rolls (for example, intermediate rolls) than the work rolls are rendered to operate as drive rolls.
In the above mill structure, the work rolls are each subjected during the rolling operation to a driving tangential force from an roll (for example, an intermediate roll) contacting with the work roll, and a front tension and a back tension from a plate under rolling. These force and tensions are all forces acting on the work roll in the horizontal direction (referred to as horizontal forces hereinafter). On the other hand, the smaller the diameter of the work roll, the smaller is the bending rigidity of the roll itself. Accordingly, the work roll undergoes deflection in a horizontal plane due to the horizontal forces.
The horizontal deflection causes a more marked disturbance in shape (flatness) of a plate under rolling. Also, when upper and lower work rolls deflect in opposite directions (one deflecting toward the incoming side and the other deflecting toward the outgoing side), central portions of upper and lower work rolls are subjected to forces acting in directions away from each other, thus accelerating the deflections of the work rolls in the opposite directions. In that case, if an excessively large rolling load is applied, it would be hard to surely prevent breakage of the rolls. The rolling load cannot be therefore so increased.
To cope with the problem mentioned above, there have been developed cluster-mill type rolling mills, including a Sendzimir mill, as well as a rolling mill provided with a horizontal deflection preventing mechanism wherein barrel portions of work rolls are supported horizontally by support rolls, as disclosed in JP,A,60-18206, for example. In these rolling mills, however, since the support roll is divided in the direction of length of the roll barrel, another problem occurs in that the surface properties of the plate being deteriorate due to mark transfer made by the divided support rolls.
For solving the above problem, JP,A,2-147108, for example, discloses a rolling mill wherein barrel portions of work rolls are supported horizontally by not-divided support rolls, and barrel portions of the support rolls are supported by hydrostatic pressure bearings, thereby suppressing deflections of the work rolls.